The disclosure of Japanese Patent Application No. 11-235958 filed on Aug. 23, 1999 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of Invention
The invention relates to a direct-fuel-injection-type spark-ignition internal combustion engine having, in an upper wall of a cylinder, a cavity for forming a combustible air-fuel mixture, and to a method of injecting fuel with such an engine.
2. Description of Related Art
Typically, a direct-fuel-injection-type spark-ignition internal combustion engine having a fuel injection valve for injecting fuel directly into a cylinder injects fuel into a cavity formed in a top surface of a piston during a late period of the compression stroke so as to vaporize fuel using heat from the piston and to guide the vaporized fuel to the vicinity of an ignition plug so that, at the time of ignition, a combustible air-fuel mixture with a good ignition quality is formed only in the vicinity of the ignition plug. The engine thus realizes stratified charge combustion that allows combustion of a mixture that is fuel-lean in terms of the entire cylinder.
In this kind of direct-fuel-injection-type spark-ignition internal combustion engine, the fuel injection timing is limited by the piston position in order to reliably inject fuel into the cavity, so that the freedom in fuel injection is low. Therefore, when the piston rising speed during the compression stroke becomes high as the engine revolution speed increases, the time between the lowermost piston position where fuel injection is allowed and the ignition timing becomes particularly short so that it becomes difficult to form a good combustible mixture. To solve this problem, Japanese Patent Application Laid-Open No. 60-261922 proposes increasing the freedom in fuel injection by forming a cavity in the cylinder head.
However, even if a cavity is formed in the cylinder head and fuel is simply injected into the cavity as described above, it is not always the case that the entire amount of fuel injected has vaporized and formed a combustible mixture at the time of ignition. Furthermore, even if a combustible mixture is formed, there is a possibility that the combustible mixture is not positioned in the vicinity of the ignition plug at the time of ignition; for example, a main portion of the mixture may flow out of the cavity before the ignition.
Accordingly, a direct-fuel-injection-type spark-ignition internal combustion engine according to the invention provides a good stratified charge combustion by reliably positioning a main portion of an air-fuel mixture near an ignition plug at the time of ignition in a direct-fuel-injection-type spark-ignition internal combustion engine having, in an upper cylinder wall, a cavity for forming a combustible mixture.
To provide a good stratified charge combustion, a direct-fuel-injection-type spark-ignition internal combustion engine according to one aspect of the invention includes an ignition plug, a cavity formed in an upper wall of a cylinder, and a fuel injection valve that injects fuel so that most of the fuel strikes a side wall of the cavity at an acute angle with respect to a tangent to the side wall at the point where the fuel strikes the side wall. The side wall of the cavity has a fuel guide portion. Most of the fuel is guided along the fuel guide portion to the vicinity of the ignition plug.
In the various exemplary embodiments of the invention, most of the fuel forms a narrow and long body of combustible mixture due to heat received as it moves along the fuel guide portion. Since the narrow and long body of combustible mixture passes by the ignition plug, the combustible mixture remains in contact with the ignition plug for a relatively long time. Therefore, it becomes possible to relatively freely set the fuel injection timing and the ignition timing. Hence, the direct-fuel-injection-type spark-ignition internal combustion engine of the invention is able to reliably position a main portion of combustible mixture in the vicinity of the ignition plug at the time of ignition and therefore realize a good stratified charge combustion.
In the direct-fuel-injection-type spark-ignition internal combustion engine, the fuel injection valve may inject the main portion of the fuel separately in two directions. In this case, portions of the main portion of the fuel injected in the two directions are guided along the fuel guide portion to the vicinity of the ignition plug so as to face each other.
Furthermore, in the direct-fuel-injection-type spark-ignition internal combustion engine, at least a portion of the fuel guide portion may be adjacent to an intake port opening formed in the upper wall of the cylinder.
Still further, in the direct-fuel-injection-type spark-ignition internal combustion engine, at least a portion of the fuel guide portion may be adjacent to an exhaust port opening formed in the upper wall of the cylinder.
Still further, in the direct-fuel-injection-type spark-ignition internal combustion engine, the fuel guide portion may have a barrier portion that a liquid fuel moving along the fuel guide portion strikes in the vicinity of the ignition plug.
Further, in the direct-fuel-injection-type spark-ignition internal combustion engine, the fuel injection valve may inject the fuel as a generally flat sector-shaped (i.e. fan-shaped) fuel spray having a small thickness. In this case, a central portion of the sector-shaped fuel spray in a direction of a width of the sector-shaped fuel spray is directed substantially toward a center axis of the ignition plug.